Preparation of polymethacrylate / alkyl naphthalene compound anticoagulant and application of polymethacrylate / alkyl naphthalene compound anticoagulant in synthetic ester insulating oil

Abstract

The invention discloses preparation of a polymethacrylate / alkyl naphthalene compound anticoagulant and application of the polymethacrylate / alkyl naphthalene compound anticoagulant in synthetic ester insulating oil, and relates to the technical field of synthetic ester insulating oil. The preparation method comprises the following steps: mixing beta-naphthol with straight-chain alpha-olefin, carrying out alkylation reaction to obtain beta-(C10-C14 alkyl) naphthalene, and compounding polymethacrylate with the beta-(C10-C14 alkyl) naphthalene to obtain the polymethacrylate / alkyl naphthalene compound anticoagulant for the insulating oil. The Mn of the polymethacrylate is 8000-12000g / mol, and the PDI is less than or equal to 1.2; and the straight chain alpha-olefin is one or more of C10-C14 straight chain alpha-olefin. Through synergistic compounding design of narrow-distribution polymethacrylate and beta-alkyl naphthalene, the comprehensive performance of the synthetic ester insulating oil is remarkably improved, and the technical problem that an existing anticoagulant is difficult to consider low-temperature fluidity, oxidation stability and insulating performance at the same time is solved.

Description

Technical Field

[0001] This invention relates to the field of synthetic ester insulating oil technology, and in particular to the preparation of polymethacrylate / alkylnaphthalene compound anti-gelling agents and their application in synthetic ester insulating oils. Background Technology

[0002] Insulating oil is the core functional medium in power transmission and transformation equipment such as transformers and reactors, and it must simultaneously undertake critical tasks such as insulation, heat dissipation, and fault arc suppression. Traditional mineral insulating oil is widely used due to its advantages of high dielectric strength and low cost. However, its inherent defects gradually become apparent under harsh operating conditions such as high temperature and high load: First, mineral oil generally has a pour point higher than -30℃. Its viscosity increases sharply at low temperatures, leading to a significant decrease in oil circulation efficiency and easily causing local overheating or even insulation failure in equipment. Second, the free radical chain reaction generated by thermal oxidation during operation is difficult to suppress, which accelerates oil aging and generates carboxylic acid substances, corroding the equipment's insulating paper and significantly shortening the equipment's service life. Furthermore, mineral oil has extremely low biodegradability, and its environmental residence time can even exceed several decades. Leaks can easily cause soil and water pollution, making it difficult to meet the urgent needs of the global power transmission and transformation industry for green and sustainable development.

[0003] To overcome the aforementioned technical bottlenecks, synthetic ester insulating oils (such as polyol esters and complex esters) have achieved a leap in performance through molecular structure design. Their biodegradability (OECD 301B standard degradation rate >90%), high flash point (>300℃), and long oxidation induction period (>120h@120℃) are significantly superior to mineral oils, making them the mainstream research direction for environmentally friendly insulating oils. However, the presence of polar ester groups in synthetic ester molecules makes them prone to forming ordered crystalline networks through hydrogen bonding at low temperatures. Even with basic formula optimization, the pour point of typical products remains limited to -40℃ to -45℃, failing to meet the stringent low-temperature fluidity requirements of power transmission and transformation equipment in extremely cold regions (such as -55℃ to -60℃ environments).

[0004] In existing technologies, improvements to the low-temperature performance of synthetic esters mainly rely on single-component anticoagulants: one type is polymethacrylate polymers, which inhibit crystallization through steric hindrance, but when the addition amount exceeds 1.5wt%, the breakdown voltage of the oil will drop by more than 15% due to molecular chain entanglement, seriously threatening the insulation safety of equipment; the other type is alkylbenzene aromatic compounds, which can reduce the crystallization phase transition temperature to improve low-temperature fluidity, but their free radical quenching ability is insufficient, and they cannot synergistically improve the oxidation stability of the oil. Moreover, short-chain alkylbenzene derivatives face strict environmental regulations due to ecotoxicity controversies.

[0005] Therefore, developing a compound anti-gelling agent system that can simultaneously enhance low-temperature fluidity and synergistically improve oxidation stability without compromising the inherent insulating properties of synthetic esters has become a key technological challenge to overcome the barriers to the extremely cold application of environmentally friendly insulating oils and promote their large-scale replacement of traditional mineral oils. Summary of the Invention

[0006] The purpose of this invention is to provide the preparation of polymethacrylate / alkylnaphthalene compound anticoagulant and its application in synthetic ester insulating oil, so as to solve the problems existing in the prior art.

[0007] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is to provide a method for preparing a polyoxymethylene acrylate / alkylnaphthalene composite anti-gelling agent for insulating oil, comprising the following steps: (1) Preparation of polymethyl methacrylate (PMA): Methyl methacrylate monomer, chain transfer agent and initiator are dissolved in solvent and polymerized under nitrogen protection. After fractional precipitation in a hexane / acetone mixed solvent, polymethyl methacrylate (PMA) with number average molecular weight Mn=8000-12000 g / mol and molecular weight distribution index PDI≤1.2 is obtained. (2) Preparation of β-alkylnaphthalene: β-naphthol and straight-chain α-olefin are mixed in a molar ratio of 1:2-3, and a catalyst is added to carry out an alkylation reaction. The reaction solution is washed with alkali and water to obtain β-(C10-C14 alkyl)naphthalene; the straight-chain α-olefin is one or more of C10-C14 straight-chain α-olefins.

[0008] (3) Compounding: The polymethyl methacrylate prepared in step (1) and the β-(C10-C14 alkyl)naphthalene prepared in step (2) are compounded at a mass ratio of 2:1-4:1 to obtain the polymethyl methacrylate / alkylnaphthalene compound anticoagulant for insulating oil.

[0009] In this invention, β-(C10-C14 alkyl)naphthalene refers to β-alkylnaphthalene with 10 to 14 carbon atoms in the alkyl chain. It can be a single β-alkylnaphthalene or a mixture of β-alkylnaphthalenes with different carbon numbers.

[0010] The PMA generated by the polymerization reaction naturally exhibits differences in molecular weight and has a wide molecular weight distribution. Different molecular weights of PMA have different effects on the performance of insulating oil. Therefore, classification is a key step in this invention to achieve precise control of PMA molecular weight (Mn=8000-12000g / mol, PDI≤1.2), laying the foundation for subsequent synergistic effects with β-alkylnaphthalene.

[0011] In a specific embodiment of this invention, a hexane / acetone mixed solvent is used for precipitation classification. This utilizes the different solubilities of PMA with different molecular weights in the mixed solvent: hexane is a poor solvent for PMA, while acetone is a good solvent. By controlling the volume ratio of the two, the solvent's solubility in PMA can be adjusted. After the polymerization reaction solution is injected into this mixed solvent, high molecular weight PMA precipitates preferentially due to its low solubility, while low molecular weight PMA remains dissolved in the solvent. Through filtration and separation, non-target components can be removed, retaining only the target molecular weight PMA with matching solubility, thus achieving molecular weight classification and screening.

[0012] This invention ultimately obtains PMA with a narrow molecular weight distribution: on the one hand, it ensures that the PMA molecular chain length is uniform and the steric hindrance effect is concentrated, which can effectively suppress the low-temperature crystallization of synthetic ester insulating oil; on the other hand, it avoids performance fluctuations (such as pour point rebound and breakdown voltage drop) caused by an excessively wide molecular weight distribution, and ensures the synergistic stability of the compound system.

[0013] The main chain structure of polymethyl methacrylate (PMMA) is a linear polymer chain formed by the free radical polymerization of methyl methacrylate monomers. The main chain consists of a repeating carbon-carbon skeleton (-CH2-C(CH3)(COOCH3)-). The side chains are characterized by each repeating unit carrying a methyl (-CH3) and a methoxycarbonyl (-COOCH3) side group, forming a sterically hindered structure. The alkylnaphthalene core structure consists of a naphthalene ring (two fused benzene rings) with a long-chain alkyl group (such as a C12 straight-chain alkyl group -C) attached to the β-position (position 2). 12 H 25 This forms a planar aromatic ring-flexible alkyl chain composite structure.

[0014] Further, in step (1), the chain transfer agent includes dodecyl mercaptan; the initiator includes azobisisobutyronitrile.

[0015] Further, in step (1), the solvent includes toluene; the polymerization reaction temperature is 80°C and the reaction time is 5-7 h.

[0016] Furthermore, in step (2), the alkylation reaction is carried out at a temperature of 170-190°C for 4-6 hours and at a pressure of 1.5-2.5 MPa. The catalyst used in the alkylation reaction is concentrated sulfuric acid.

[0017] Furthermore, when the straight-chain α-olefin is one of multiple C10-C14 straight-chain α-olefins, the molar percentage of C12 straight-chain α-olefins in the straight-chain α-olefin is ≥40%; more preferably, the molar percentage is ≥60%.

[0018] In this invention, the amount of chain transfer agent added is 0.3-0.7 wt% of the mass of methyl methacrylate monomer, and the amount of initiator added is 0.6-1.0 wt% of the mass of methyl methacrylate monomer; the volume ratio of the n-hexane / acetone mixed solvent is 4-6:1.

[0019] In step (2), the reaction solution is washed with alkali and water, and then purified by molecular distillation to obtain β-(C10-C14 alkyl)naphthalene; the conditions for molecular distillation are 190-210℃ and 3-7 Pa, and the purity of β-(C10-C14 alkyl)naphthalene after purification is ≥95%.

[0020] Furthermore, the β-alkylnaphthalene is a doped β-(C10-C14 alkyl)naphthalene, and the preparation steps of the polyacrylate / alkylnaphthalene compound anti-coagulant for insulating oil are as follows: Preparation of doped β-(C10-C14 alkyl)naphthalene: β-naphthol is mixed with the straight-chain α-olefin at a molar ratio of 1:2-3. During the alkylation reaction with the addition of a catalyst, the reaction solution is washed with alkali and water to obtain β-(C10-C14 alkyl)naphthalene; the β-(C10-C14 alkyl)naphthalene is then mixed with short-chain alkyl groups to obtain doped β-(C10-C14 alkyl)naphthalene. Compounding: Polymethacrylate and doped β-(C10-C14 alkyl)naphthalene are compounded at a mass ratio of 2:1-4:1 to form a polymethacrylate / alkylnaphthalene compound anti-gelling agent for insulating oil.

[0021] Furthermore, the doping amount of the short-chain alkyl group in the doped β-alkylnaphthalene is ≤10%; the short-chain alkyl group is a C8 alkyl group.

[0022] The second technical solution of the present invention provides a polymethacrylate / alkylnaphthalene composite anticoagulant prepared by the above preparation method.

[0023] The third technical solution of the present invention provides the application of the above-mentioned polyoxymethylene acrylate / alkylnaphthalene compound anticoagulant in the anticoagulant function of insulating oil.

[0024] Furthermore, the total amount of the polymethacrylate / alkylnaphthalene compound anti-gelling agent added to the insulating oil is ≤1.5wt%.

[0025] Furthermore, the basic synthetic ester oil is a polyol ester, which includes pentaerythritol tetraisooctanoate.

[0026] The fourth technical solution of the present invention provides a synthetic ester insulating oil, comprising the above-mentioned polymethacrylate / alkylnaphthalene compound anticoagulant.

[0027] Furthermore, the mass content of the polymethacrylate / alkylnaphthalene compound anticoagulant in the synthetic ester insulating oil is ≤1.5 wt%.

[0028] Fifth technical solution of the present invention: providing a method for preparing the above-mentioned synthetic ester insulating oil, comprising the following steps: The polymethacrylate / alkylnaphthalene compound anticoagulant was added to the synthetic ester oil insulating oil and dispersed.

[0029] Furthermore, ultrasonic dispersion at 50-70℃ with a power of ≥250 W for ≥20 minutes.

[0030] The present invention discloses the following technical effects: This invention achieves a significant improvement in the overall performance of synthetic ester insulating oil through a synergistic compound design of narrow-distribution polymethacrylate (PMA) and β-alkylnaphthalene, effectively solving the technical problem that existing anti-gelling agents cannot simultaneously achieve low-temperature fluidity, oxidation stability, and insulation performance. In the compound system, the steric hindrance effect of the long chain of PMA molecules complements the crystallization inhibition effect of β-alkylnaphthalene, resulting in a significant reduction in the pour point of the insulating oil and a significant optimization of its low-temperature kinematic viscosity, making it stable and adaptable to extremely cold operating conditions from -55℃ to -60℃. At the same time, the rigid aromatic ring structure of β-alkylnaphthalene and the good molecular compatibility of PMA construct a highly efficient synergistic antioxidant mechanism, significantly extending the equipment operation and maintenance cycle.

[0031] The anti-coagulation agent of this invention ensures that the core insulation performance such as the breakdown voltage of the insulating oil meets the standards, while maintaining an excellent biodegradability rate to meet green and environmental protection requirements. It provides key technical support for the large-scale replacement of traditional mineral oil with synthetic ester insulating oil and the expansion of its application in power transmission and transformation equipment in high-altitude and cold regions. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a comparison graph showing the kinematic viscosity of Example 1 (PMA / β-alkylnaphthalene complex system) and Comparative Examples 1-2 (single anticoagulant system) as a function of temperature. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0038] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0039] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0040] The present invention will be further described in detail below with reference to embodiments. To ensure that the compounded anti-gelling agent fully exerts its synergistic effect in the synthetic ester insulating oil, and to guarantee the ultra-low pour point, high oxidation stability, and excellent dielectric properties of the target insulating oil, the following key parameters must be strictly controlled during implementation: (1) Molecular weight and distribution of PMA: The number average molecular weight (Mn) of polymethyl methacrylate (PMA) needs to be controlled within the range of 10000±2000 g / mol, and the molecular weight distribution index (PDI) should be ≤1.2. If the molecular weight of PMA exceeds 15000 g / mol, the breakdown voltage of the insulating oil will decrease by ≥5%; if the PDI is >1.5, the pour point of the oil will rise to above -53℃, which cannot meet the requirements for use in extremely cold environments.

[0041] (2) Control of branched structure of β-alkylnaphthalene: The proportion of C12 alkyl in β-alkylnaphthalene must be ≥40% (more preferably ≥60%), and the doping amount of short-chain alkyl (such as C8) must not exceed 10%. If this branching ratio requirement is not met, the free radical quenching ability of β-alkylnaphthalene will decrease, the oxidation induction period of insulating oil will be shortened, and the oxidation stability will be significantly worse.

[0042] (3) Control the accuracy of the compounding ratio: The mass ratio of PMA to β-alkylnaphthalene must be strictly controlled between 2:1 and 4:1. If the ratio exceeds this range, it will cause the pour point of the insulating oil to rise, and the breakdown voltage to drop, thus losing the synergistic advantage of low-temperature performance and insulation performance.

[0043] (4) Control the dispersion process parameters: After the compound anticoagulant is added to the base synthetic ester oil, the ultrasonic dispersion power should be ≥250 W and the dispersion time should be ≥20 minutes. If the ultrasonic power is insufficient or the dispersion time is too short, the anticoagulant particles are prone to agglomeration, which will affect the stability of low-temperature fluidity.

[0044] Example 1: Preparation of PMA / β-alkylnaphthalene compound anticoagulant. This embodiment provides a PMA / β-alkylnaphthalene compound anticoagulant, and the preparation steps are as follows: S1. Preparation of PMA by molecular weight fractionation: In a nitrogen-protected polymerization reactor, 100 g of methyl methacrylate monomer, 0.5 wt% of chain transfer agent dodecyl mercaptan, and 0.8 wt% of initiator azobisisobutyronitrile were added, and the above materials were dissolved in 200 mL of toluene. The reaction system was then heated to 80 °C and reacted at this temperature for 6 hours. After the reaction was completed, the reaction solution was cooled and injected into a 5:1 (v / v) hexane / acetone mixed solvent for fractional precipitation. After separation, polymethyl methacrylate (PMA) with a narrow molecular weight distribution was obtained, with a number average molecular weight Mn = 10000 g / mol and a molecular weight distribution index PDI = 1.1.

[0045] S2, β-alkylnaphthalene branching optimization: 1 mol of β-naphthol and 2.5 mol of C12 straight-chain α-olefin were added to a high-pressure reactor, followed by 2 wt% concentrated sulfuric acid as a catalyst. The alkylation reaction was carried out at 180℃ and 2 MPa for 5 hours. After the reaction, the reaction solution was first washed with 5% NaOH solution, then washed with deionized water until neutral, and finally purified by molecular distillation at 200℃ and 5 Pa to obtain β-(C12 alkyl)naphthalene (purity ≥98%).

[0046] S3. Anticoagulant compounding and addition process: Take the PMA prepared in step S1 and the β-(C12 alkyl)naphthalene prepared in step S2, and compound them in a mass ratio of 2:1. Add the compound system to the basic synthetic ester oil (pentaerythritol tetraisooctanoate, pour point -38℃) at an addition amount of 1.0 wt% PMA and 0.5 wt% β-(C12 alkyl)naphthalene. Disperse the mixture ultrasonically at 300W for 30 minutes at 60℃. After dispersion, filter through a 0.2μm filter membrane to obtain the target insulating oil product.

[0047] Performance testing of the target insulating oil product showed significant optimization in all aspects: According to ISO 3016 standard, the pour point was -58℃; according to IEC 60156 standard, the breakdown voltage was 67kV / 2.5mm; according to ASTM D2272 standard, the oxidation induction period at 120℃ was 185h; according to IEC 62021.3 standard, the acid value was 0.018 mgKOH / g; according to IEC 60247 standard, the dielectric loss factor at 90℃ was 0.0010; according to OECD 301B standard, the biodegradation rate was 92%; and according to ISO 3104 standard, the kinematic viscosity at -30℃ was 3200mm² / s.

[0048] Example 2: Preparation of PMA / β-alkylnaphthalene compound anticoagulant This embodiment provides a PMA / β-alkylnaphthalene compound anticoagulant, and the preparation steps are as follows: S1, PMA molecular weight control: Same as step S1 in Example 1, except that the amount of chain transfer agent dodecyl mercaptan is adjusted to 0.3 wt%, and finally a high molecular weight polymethyl methacrylate (PMA) is obtained with a number average molecular weight Mn = 12000 g / mol and a molecular weight distribution index PDI = 1.15.

[0049] S2, Preparation of mixed branched β-alkylnaphthalene: 1 mol of β-naphthol, and C10 straight-chain α-olefin, C12 straight-chain α-olefin and C14 straight-chain α-olefin (total amount 2.5 mol) in a molar ratio of 3:4:3 were added to a high-pressure reactor, followed by 2 wt% concentrated sulfuric acid as a catalyst. The alkylation reaction was carried out under the same conditions as in Example 1 (180℃, 2 MPa for 5 hours). After the reaction was completed, the mixture was washed with 5% NaOH solution and deionized water until neutral, and then purified by molecular distillation (200℃, 5 Pa) to obtain β-(C10-C14 mixed alkyl)naphthalene (purity ≥95%).

[0050] S3. Compounding: Take the PMA prepared in step S1 and the β-(C10-C14 mixed alkyl)naphthalene prepared in step S2, and compound them at a mass ratio of 2:1. According to the ratio of 1.0wt% of PMA and 0.5wt% of β-(C10-C14 mixed alkyl)naphthalene, add the compound system to the same basic synthetic ester oil (pentaerythritol tetraisooctanoate, pour point -38℃) as in Example 1. The dispersion process is the same as in Example 1 (ultrasonic dispersion at 300W power for 30 minutes at 60℃). After dispersion, filter through a 0.2μm filter membrane to obtain the target insulating oil product.

[0051] Performance testing of the target insulating oil product revealed significant improvements in various properties: pour point of -59℃ according to ISO 3016; acid value of 0.018 mgKOH / g according to IEC 62021.3; dielectric loss factor of 0.0009 at 90℃ according to IEC 60247; breakdown voltage of 68 kV / 2.5 mm according to IEC 60156; oxidation induction period of 160 h at 120℃ according to ASTM D2272; biodegradability of 92% according to OECD 301B; and kinematic viscosity of 2800 mm² / s at -30℃ according to ISO 3104.

[0052] Example 3: Preparation of PMA / β-alkylnaphthalene compound anticoagulant This embodiment provides a PMA / β-alkylnaphthalene compound anticoagulant, and the preparation steps are as follows: S1. Preparation of Ultra-Narrow Molecular Weight PMA: In a nitrogen-protected polymerization reactor, 100g of methyl methacrylate monomer, 0.5wt% of chain transfer agent dodecyl mercaptan, and 0.8wt% of initiator azobisisobutyronitrile were added, and the above materials were dissolved in 200mL of toluene. The reaction system was then heated to 80℃ and reacted at a constant temperature for 6 hours. After the reaction, the reaction solution was cooled, and a two-stage precipitation method using a hexane / acetone gradient elution was adopted. Specifically: First precipitation: The reaction solution was first injected into a mixed solvent of hexane / acetone with a volume ratio of 4:1, so that the extremely high molecular weight fraction preferentially precipitated out, and the precipitate was removed by filtration; Second precipitation: Hexane was then added to the filtrate to adjust the volume ratio of the mixed solvent to 6:1. At this time, PMA with the target narrow molecular weight distribution range (Mn=9500) precipitated out, and the final product was obtained after separation and drying. The final product was polymethyl methacrylate (PMA) with an ultra-narrow molecular weight distribution, with a number-average molecular weight Mn = 9500 g / mol and a molecular weight distribution index PDI = 1.05.

[0053] S2, Short-chain β-alkylnaphthalene doping: β-(C12 alkyl)naphthalene was prepared using the same steps as in Example 1. Then, 10% of C8 short-chain alkyl (β-octylnaphthalene) was added to the β-(C12 alkyl)naphthalene. After uniform mixing, doped β-alkylnaphthalene was obtained, achieving a balance between low-temperature fluidity and oxidation stability.

[0054] S3. Anticoagulant compounding: Take the ultranarrow molecular weight PMA prepared in step S1 and the doped β-alkyl naphthalene prepared in step S2, and compound them at a mass ratio of 4:1. According to the ratio of 1.2wt% PMA and 0.3wt% doped β-alkyl naphthalene, add the compounding system to the same basic synthetic ester oil (pentaerythritol tetraisooctanoate, pour point -38℃) as in Example 1. The dispersion and filtration treatment are the same as in Example 1 (ultrasonic dispersion at 300W power for 30 minutes at 60℃, and filtration through a 0.2μm filter membrane) to obtain the target insulating oil product.

[0055] Performance testing of the target insulating oil product revealed significant improvements in its overall performance: According to ISO 3016, the pour point was -57℃; according to IEC 62021.3, the acid value was 0.035 mgKOH / g; according to IEC 60247, the dielectric loss factor at 90℃ was 0.015; according to IEC 60156, the breakdown voltage was 67kV / 2.5mm; according to ASTM D2272, the oxidation induction period at 120℃ was 140h; according to OECD 301B, the biodegradation rate was 89%; and according to ISO 3104, the kinematic viscosity at -30℃ was 3100mm² / s.

[0056] Comparative Example 1: Preparation of a single PMA anticoagulant system The only difference from Example 1 is that 1.5 wt% PMA was added to the basic synthetic ester oil (pentaerythritol tetraisooctanoate, pour point -38°C), that is, β-(C12 alkyl)naphthalene was replaced with an equal amount of PMA; and the PMA preparation process was the same as in Example 1. An insulating oil modified with a single PMA anti-gelling agent was obtained.

[0057] The performance test results are as follows: According to ISO 3016 standard, the pour point is -45℃; according to ISO 3104 standard, the kinematic viscosity at -30℃ is 4100 mm² / s; according to IEC 60156 standard, the breakdown voltage is 64 kV / 2.5 mm; according to IEC 60247 standard, the dielectric loss factor at 90℃ is 0.0020; according to ASTM D2272 standard, the oxidation induction period at 120℃ is 90 h; according to IEC 62021.3 standard, the acid value is 0.12 mg KOH / g; according to OECD 301B standard, the biodegradability rate is 85%.

[0058] Comparative Example 2: Single β-alkylnaphthalene anticoagulant system The only difference from Example 1 is that 1.5 wt% of β-(C12 alkyl) was added to the base synthetic ester oil (pentaerythritol tetraisooctanoate, pour point -38°C); and the PMA preparation process was the same as in Example 1. An insulating oil modified with a single β-(C12 alkyl) anti-gelling agent was obtained.

[0059] The performance test results are as follows: According to ISO 3016 standard, the pour point is -48℃; according to ISO 3104 standard, the kinematic viscosity at -30℃ is 3500 mm² / s; according to IEC 60156 standard, the breakdown voltage is 66 kV / 2.5 mm; according to IEC 60247 standard, the dielectric loss factor at 90℃ is 0.0018; according to ASTM D2272 standard, the oxidation induction period at 120℃ is 120 h; according to IEC 62021.3 standard, the acid value is 0.08 mg KOH / g; according to OECD 301B standard, the biodegradability rate is 88%.

[0060] Using the same base synthetic ester oil (pour point -38℃) without added anticoagulant as a benchmark, the performance of the single anticoagulant systems of Comparative Examples 1 and 2 and the compound system of this invention were compared and tested: Table 1 compares the physicochemical parameters of Example 1, Comparative Examples 1-2, and the base oil. It can be seen that by compounding polymethyl methacrylate (PMA) and β-alkylnaphthalene, the synergistic effects of steric hindrance and free radical quenching are achieved, enabling the synthetic ester insulating oil to achieve a pour point below -58°C and an oxidation induction period of 185 h (270% higher than the base oil), while maintaining dielectric strength (67 kV / 2.5 mm) and achieving a 92% biodegradability rate. This invention overcomes the challenge of synergistically optimizing low-temperature crystallization, oxidative aging, and environmental friendliness of insulating oil in extremely cold environments, providing a low-temperature adaptability and green compliance insulating oil solution for power transmission and transformation equipment in high-altitude and cold regions.

[0061] Table 1 When only 1.5 wt% polymethyl methacrylate (PMA, number average molecular weight Mn=10000 g / mol) is added to the base oil, the pour point of the oil decreases to -45℃, the oxidation induction period at 120℃ is 90h, and the breakdown voltage is 64kV / 2.5mm. When only 1.0 wt% β-(C12 alkyl)naphthalene is added, the pour point of the oil is slightly better than that of the single PMA system, improving to -48℃, and the oxidation induction period is extended to 120h, but the breakdown voltage only increases to 66kV / 2.5mm.

[0062] In contrast, the compound system of Example 1 of this invention (1.0wt% PMA + 0.5wt% β-(C12 alkyl)naphthalene) achieved a synergistic leap in performance, with a pour point significantly reduced to -58℃, an oxidation induction period of 185h at 120℃, and a breakdown voltage as high as 67kV / 2.5mm, without exhibiting the dielectric strength reduction problem present in single additive systems.

[0063] The above comparative results show that the compound system of PMA and β-alkylnaphthalene not only breaks through the performance limit of single anticoagulants in low-temperature fluidity, but also achieves simultaneous optimization of the oxidation stability and insulation performance of synthetic ester insulating oil through the synergistic effect of free radical quenching (β-alkylnaphthalene effect) and molecular entanglement inhibition (PMA effect), solving the problem that single additives in the existing technology cannot take into account multiple core performance aspects.

[0064] Figure 1 shows a comparison of the kinematic viscosity of Example 1 (PMA / β-alkylnaphthalene compound system) and Comparative Examples 1-2 (single anticoagulant systems) as a function of temperature. Comparative Example 1 is labeled as Comparative Example-PMA, and Comparative Example 2 is labeled as Comparative Example-alkylnaphthalene. The figure clearly shows that the compound system of Example 1 exhibits superior viscosity-temperature adaptability through the synergistic effect of PMA and β-alkylnaphthalene: on the one hand, it leverages the excellent flow-promoting properties of the long PMA molecular chain; on the other hand, it effectively suppresses molecular breakage and oxidation reactions under high-temperature conditions by utilizing the rigid aromatic ring skeleton of β-alkylnaphthalene.

[0065] Specifically, under low-temperature conditions, the molecules of PMA and β-alkylnaphthalene interpenetrate to form a complementary molecular network structure, which significantly weakens the aggregation tendency and crystallization tendency of synthetic ester molecules. This results in a 20%–30% reduction in the kinematic viscosity of the oil at -30℃ compared to a single PMA system or a single alkylbenzene system, greatly improving low-temperature fluidity. In a high-temperature environment of 40℃, the thermal stability of β-alkylnaphthalene further enhances the oil's resistance to thermal oxidation, not only making the viscosity-temperature curve more gentle but also effectively suppressing the viscosity increase caused by long-term operation, ensuring stable performance under different temperature conditions.

[0066] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a polymethacrylate / alkylnaphthalene composite anti-gelling agent for insulating oil, characterized in that, Includes the following steps: Preparation of β-alkylnaphthalene: β-naphthol and straight-chain α-olefins are mixed in a molar ratio of 1:2-3, and a catalyst is added to carry out an alkylation reaction. After the reaction is completed, the mixture is washed with alkali and water to obtain β-alkylnaphthalene, namely β-(C10-C14 alkyl)naphthalene. Compounding: Polymethacrylate and β-(C10-C14 alkyl)naphthalene are compounded at a mass ratio of 2:1-4:1 to obtain the polymethacrylate / alkylnaphthalene compound anti-gelling agent for insulating oil; The polymethacrylate has a number-average molecular weight Mn of 8000-12000 g / mol and a molecular weight distribution index PDI ≤ 1.

2. The straight-chain α-olefin is one or more of C10-C14 straight-chain α-olefins.

2. The preparation method according to claim 1, characterized in that, The alkylation reaction is carried out at a temperature of 170-190℃ for 4-6 hours; the catalyst used in the alkylation reaction is concentrated sulfuric acid.

3. The preparation method according to claim 1, characterized in that, When the straight-chain α-olefin is one of multiple C10-C14 straight-chain α-olefins, the molar percentage of C12 straight-chain α-olefins in the straight-chain α-olefin is ≥40%.

4. The preparation method according to claim 1, characterized in that, The β-alkylnaphthalene is a doped β-(C10-C14 alkyl)naphthalene. The preparation steps of the polymethyl methacrylate / alkylnaphthalene compound anti-gelling agent for insulating oil are as follows: Preparation of doped β-(C10-C14 alkyl)naphthalene: β-naphthol was mixed with the straight-chain α-olefin at a molar ratio of 1:2-3, and a catalyst was added to carry out an alkylation reaction. The reaction solution was washed with alkali and water to obtain β-(C10-C14 alkyl)naphthalene. Then, the β-(C10-C14 alkyl)naphthalene was mixed with short-chain alkanes to obtain doped β-(C10-C14 alkyl)naphthalene. Compounding: The polymethacrylate and the doped β-(C10-C14 alkyl)naphthalene are compounded at a mass ratio of 2:1-4:1 to obtain a polymethacrylate / alkylnaphthalene compound anti-coagulation agent for insulating oil.

5. The preparation method according to claim 4, characterized in that, The doping amount of the short-chain alkyl group in the doped β-alkyl naphthalene is ≤10%; the short-chain alkyl group is a C8 alkane.

6. The polymethacrylate / alkylnaphthalene composite anticoagulant prepared by any one of the preparation methods described in claims 1-5.

7. The application of the polymethacrylate / alkylnaphthalene compound anti-coking agent as described in claim 6 in the anti-coking of insulating oil.

8. The application according to claim 7, characterized in that, The total amount of the polymethacrylate / alkylnaphthalene compound anti-gelling agent added to the insulating oil is ≤1.5 wt%; the insulating oil is a synthetic ester oil insulating oil, which includes pentaerythritol tetraisooctanoate.

9. A synthetic ester insulating oil, characterized in that, Includes the polymethacrylate / alkylnaphthalene compound anticoagulant as described in claim 6.

10. The method for preparing the synthetic ester insulating oil according to claim 9, characterized in that, Includes the following steps: The polymethacrylate / alkylnaphthalene compound anticoagulant was added to the synthetic ester oil insulating oil and dispersed.

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